Blocking Popup Webpages

How can I block specific webpages that keep opening themselves in a new tab?

Hello RP,
That may be because of adware/extension/cookies of the browser. You can reset your browser once and check if you can browser without any problem. May I know which browser (like Google chrome, Mozilla Firefox, internet explorer etc) you're using on your computer, let me know the exact url which you want to block and also a screenshot of the page (which is getting opened automatically) to assist you further. You can check the following link to see the instructions about taking the screenshot (http://support.avg.com/SupportArticleView?urlname=How-to-create-a-screenshot). You can post the screenshot here in your topic. Click on 'Answer' & then click on the 'Image' [mountain symbol] & follow the instructions.
Best regards,
Alok.